1. Field of Invention
This invention relates generally to the field of spray pattern characterization and performs measurements of spatial particle distributions within a spray, which can be used to monitor a spraying process.
2. Background of the Invention
Sprays are associated with, among others, paint spraying, tablet and implant coating, aerosols for inhalation therapy, and fuel injectors. Since the uniformity and symmetry of the spray pattern is a crucial parameter in most applications, it is important to obtain detailed information on spray characteristics. Such information can be used to detect quality problems in spraying or coating processes and assist furthermore in optimizing aerosol delivery systems or atomizers used, for example, in medical coating applications.
In the prior art, several methods are used for the characterization and analysis of spray patterns.
Spray pattern characterization is often performed using the Patternation Index (P.I.). The P.I. is a measure of the circumferential uniformity and symmetry of the spray and is defined as the normalized variance from the expected mean, summed for all elements. The P.I. indicates the summation of the differences between the ideally uniform percentage and the actual percentage.
Another method is based on the Spray Uniformity Index (S.U.I). The S.U.I calculates the standard deviation of the normalized total intensities per element from the mean and indicates the standard deviation of the normalized local values. It is a measure of the spray uniformity.
A further approach is measuring the pattern shape, for instance an ellipsoid of relative uniform density, as well as the size of the pattern manually.
Yet another approach is based on manually selected regions within an image. Intensity profiles, standard deviation and the median value of the intensity distribution within an image of a spray are used to characterize a spray.
The P.I. and the S.U.I. are a measure for the overall distribution of the spray pattern, but they don't provide information on the location, size or type of asymmetries within the spray pattern. When measuring the shape, size and ratio between the longest and the shortest axes of the pattern manually, distribution densities and asymmetries within the pattern are not detected.
Because manual procedures depend on the judgment of an operator, good repeatability is difficult, if not impossible, to achieve. This is also true when intensity profiles of a user-defined area of an image are obtained. In such cases, the input pattern is based on the area selection of the operator and not on a defined criteria. In addition, a detailed evaluation of location, size, and type of asymmetries within the spray pattern cannot be performed.
In the prior art, characteristics of a spray pattern are not sufficiently quantitatively characterized. Detailed and repeatable information on location, size, and type of asymmetries within a spray pattern, which are important for spray characterization comparability, quality control, and in-situ control of spray processes are not provided. Therefore, there is a need for a new method and system that overcomes the drawbacks of methods and systems known by the prior art.